Minimum-height dipole-type vertically polarized log-periodic antenna

ABSTRACT

A vertically polarized log-period antenna of the dipole type is disclosed, in which the top ends of all the dipole elements are directly coupled to the antenna&#39;&#39;s main support catenary. The antenna&#39;&#39;s feed line is used to perform a structural support function, so as to reduce the structural load which has to be supported by the main catenary. Consequently, a catenary with reduced sag is used, thereby reducing the maximum height of the main support tower.

Inventor Gerald Eldon Solberg San Carlos, Calif.

App]. No 839,196

Filed July 7, 1969 Patented Nov. 2, 1971 Assignee Technology For Communications International Mountain View, Calif.

MINIMUM-HEIGHT DlPOLlE-TYPE VERTlCALLY POLARIZED LOG-PERIODIC ANTENNA 1 1 Claims, 4 Drawing Figs.

US. Cl 343/792.5,

343/812, 343/884, 343/886 lint. Cl ..]ll01q 11/10 Field of Search 343/7925,

[56] References Cited UNITED STATES PATENTS 1,860,052 5/1932 Peterson 343/886 X 3,179,943 4/1965 Buzbee 343/7925 3,248,475 4/1966 Veldhuis 343/7925 X 3,276,027 9/1966 Bell et al 343/7925 3,363,254 H1968 Carrell et a1. 343/7925 3,470,559 9/1969 Radford 4. 343/7925 Primary ExaminerEli Lieberman Attorney-Lindenberg, Freilich & Wasserman ABSTRACT: A vertically polarized log-period antenna of the dipole type is disclosed, in which the top ends of all the dipole elements are directly coupled to the antennas main support catenary The antennas feed line is used to perform a structural support function, so as to reduce the structural load which has to be supported by the main catenary. Consequently, a catenary with reduced sag is used, thereby reducing the maximum height of the main support tower.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband antenna and, more particularly, to a minimum-height vertically polarized log-periodic antenna.

2. Description of the Prior Art Vertically polarized log-periodic antennas of the dipole type are well known in the art. Typically, a vertically polarized logperiodic antenna or VPLPA of the dipole type includes dipole elements which are supported in a vertical plane by means of a support tower, at front pole, a main support catenary, which extends between the tower and the pole, and drop rods. Each of the dipole elements, comprising of two equal-length poles, has a physical length which is equal to one-half the wavelength k/ 2) of the frequency at which the element is to resonate and radiate most strongly. The dipole elements, hereafter are also referred to as dipoles or elements, are supported to form an array with the longest element, which is designed to radiate at the lowest frequency for which the antenna is designed, being supported'at the array back end near the tower, and the shortest element, corresponding to the highest frequency in the frequency band, being supported at the array front end, near the frontpole. The bottom end of each element is connected to the ground, or any other corresponding surface, through an appropriate electrical insulator, while the elements top end is connected to the catenary through a drop rod from which the element is electrically insulated. Feed wires, forming a feed line, which extend in a straight line across the array, are connected to each element at the element center to excite the element electrically, which hereafter may be referred to as electrically coacting therewith.

The space occupied by the lower portion of the array below the feed line in the vertical plane may be thought of as occupying an area in the shape of a right-angle triangle. Therein, the ground which is assumed to be level, represents one triangle side, the part of the tower below the feed line represents another side of the triangle. The feed line represents the triangle's hypotenuse.

As should be appreciated by those familiar with the art, the presence of the drop rods contributes to a significant increase in the size of the antenna and load support requirements ofthe antennas support structure. This is true for several reasons. First, the total weight of the drop rods increases the overall antenna weight, which the support structure has to support. Secondly, the drop rods, like the active elements, have an inherent resistance to wind and other environmental phenomena. Consequently, the added resistance of the drop rods has to be accounted for in designing the antennas support structure. Thirdly, the drop rods increase the overall antennas height and, therefore, necessitate the use of a higher tower than would be needed in their absence. The latter disadvantage is often very significant. It is for this reason that manufacturing sources of such antennas use minimum tower height characteristics of their antennas as a major selling point.

Another major disadvantage of the prior art vertically polarized log-periodic antenna is the limited use made of the fed line in such an antenna. Heretofore, the feed line was used only for electrical purposes. However, the feed line, like active dipole elements and the drop rods, does not have an insignificant weight. Furthermore, since it represents a certain amount of wind resistance, it not only does not contribute to the support of the antenna, but rather it represents an added load, which the antenna's support structure must be designed to sustain. Consequently, a need exists for a new approach in the design of a vertically polarized log-periodic antenna (VPLPA) which would lead to a reduction in the antenna size as well as to a reduction in the load support requirements of the antenna's support structure.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a new vertically polarized log-periodic antenna with new improved structural support characteristics.

Another object of the invention is to provide a vertically polarized log-periodic antenna with a feed line which contributes to the antenna support rather than represents an added load therefor.

A further object of the invention is to provide a vertically polarized log-periodic antenna which is supportable by a support structure which is lower than the support structure of a comparable antenna, constructed by conventional prior art design techniques.

Still a further object of the invention is to provide a vertically polarized log-periodic antenna in which the requirement for drop rods is greatly reduced.

Still another object of the invention is to provide improvements in the design and the use made of afeed line in a vertically polarized log-periodic antenna which results in a reduction in height, size and/or number ofrequired support towers.

These and other objects of the invention are achieved by providing a vertically polarized log periodic antenna (VPL- PA), in which the feed wires, formingrthe' feed line, rather than being straight and used for electrical purposes only, as is the case in the prior art, are constructed to 'serve as a feed line support catenary, hereafter referred to as a feed line catenary, in addition to performing their conventional electrical function. By such a design the feed wires not only do not add to the structural load which the antennas support structure has to support or sustain, but rather they reduce the load requirements of such structure.

By constructing the feed wires, in accordance with the teachings of the present invention, to serve as a support catenary, an additional significant advantage is realized. Such a structure enables one to construct the main'support catenary, so that it is directly connected to the tops of the various active dipole elements. Consequently, the need for drop rods between the catenary and the feed wires is eliminated. Consequently, the overall height of the antenna is reduced, thereby enabling it to be supported by a shorter tower than is required for a comparable prior art antenna.

In practice, the antenna is designed so that the longest dipole element, corresponding to the lowest frequency in the design bandwidth, is connected between the main support catenary and ground. The overall antenna structural load is distributed between the feed wires, which serve as a feed line catenary and the main support catenary, so that the vertical component of the latter in the vertical direction between the longest dipole and the tower is small. Consequently, the tower height is very close though always greater than the height or length of the longest dipole. Alternately stated, by employing the feed wires to act as a feed line catenary, the support requirements of the mainsupport catenary are reduced. Consequently, a main support catenary with less sag can beemployed, resulting in a reduction in tower height.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side view of a conventional vertically polarized dipole-type log-periodic antenna;

FIGS. 2 and 3 areisometric and side views, respectively, of the novel vertically polarized log-periodic antenna of the present invention; and

FIG. 4 is a partial isometric view of a section of the feed line and a few of the radiating dipoles, shown in FIGS. 2 and 3.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS Before proceeding to describe the novel features of the present invention, and its significant advantages, reference is first made to FIG. 1, which is a side view of a typical prior art vertically polarized log-periodic antenna of the dipole type, hereafter simply referred to as the prior art VPLPA. The prior art VPLPA, generally designated by numeral 10, is assumed to be supported in a vertical plane above a reference surface, such as ground, designated by numeral 12. It includes a typical support structure, comprising a tower 14, a front pole 16 and a main support catenary 18, which extends downwardly from the taller tower 14 to the shorter front pole 16. A plurality of tower guys 20 are used to support tower 14 vertically above ground 12, while front pole guys 22 are used to support the front pole 16 in the vertical plane.

As is appreciated by those familiar with the art, such a prior art VPLPA includes a plurality of radiating or excitable dipole elements of different lengths, each one being of a physical length which is excitable at a different frequency in the frequency band for which the antenna is designed. Typically, and for explanatory purposes, it may be assumed that each dipole element, shown in FIG. 1, corresponds to one-half the free space wavelength at which the element is to radiate, i.e., Al 2 where k is the conventional wavelength designation.

In FIG. 1, 19 elements, designated by numerals 31-49 are diagrammed. They form a vertical log-periodic array 50, disposed so that the shortest element 31, which corresponds to the highest frequency in the frequency band is positioned at a front end of the array, near front pole 16, while the longest element 49, corresponding to the lowest frequency in the frequency band (assuming that tower 14 is inactive) is disposed at the back end of the array. Each element has its lower or bottom end, designated by the elements reference numeral followed by the letter a, directly connected to ground 12 in electrical insulation therefrom. The top end of each element, designated by the element's reference numeral followed by the letter b is connected to the main support catenary 18, through a respective drop rod, which is designated by the element's reference numeral followed by the letter 0. Each of the radiating dipole elements, which in practice comprises a pair of poles, is connected electrcially, at its center, to feed wires which form the feed line, designated by reference numeral 55. In FIG. 1 as well as in the other figures, electrical connections are represented by solid dots, while mechanical connections between elements which are electrically insulated from one another are represented by small hollow circles.

As is appreciated, in such an array, the locus of all the top ends of the elements is a straight line which converges with the straight line locus of the bottom elements ends at a point 60, which represents the array apex. The feed line 55 extends between the arrays front and back end in a direction along a straight line, which can be thought of as being coincident with a straight line extending from the apex 60.

The disadvantages, particularly from an antenna support structure point of view of such a prior art VPLPA have been discussed previously. Briefly, the basic disadvantage of such an antenna, is its large size and the load support requirements of its support structure. These are due to the fact that resort is made to a plurality of drop rods, which increase the overall height of the antenna, as well as its resistance to wind or other adverse environmental phenomena, thereby greatly increasing the structure load support requirements of the support structure. Also, the feed wires, which are disposed in a straight line, cannot contribute to the support of the antenna. Rather, they represent an added load which the antenna support structure must sustain.

Such disadvantages are substantially eliminated by the novel teachings of the present invention which may best be explained by referring to FIG. 2 which is an isometric view of a VPLPA constructed in accordance with the teachings of the present invention. FIG. 3 represents a side view of the novel antenna shown in FIG. 2. In these figures, elements or components, similar to these previously discussed in connection with FIG. 1, are designated by like numerals, except that in FIGS. 2 and 3, 28 rather than 19 elements are shown. Therein, numerals 31-49 and 61-69 are used to designate the 28 elements, with the last or longest element being designated by numeral 69. V

Briefly, in accordance with the teachings of the presentinvention, the feed wires 55 perform their electrical function in a manner identical with that preformed in the prior art VPL- PA, and, therefore, such functions will not be described in any detail. However, in addition, the feed wires are mechanically and structurally connected to the front pole 16, as well as to the main support tower 14 in other than a straight line therebetween so as to perform a support function. That is, the

feed wires are connected between pole 16 and tower 14 to act as a feed line support catenary, which may be designed to support not only the weight of the feed wires themselves, but some of the structural load which the various dipole elements of the array contribute to the overall load of the antenna. The feed wires, as a feed line support catenary coact, from a structural support point of view, with catenary 18 which extends from the tower 14 to the pole 16, in order to support the array in the vertical plane. The structural connections between the feed line and front pole 16 and main tower 14 are designated in FIG. 3 by 55x and 55y, respectively.

In accordance with the teachings of the present invention, the top ends of the various dipole elements are directly connected to the catenary 18 in electrical insulation therefrom, rather than through drop rods as is the case in the prior art. Since the drop rods are eliminated, the overall height of the antenna is significantly reduced and, therefore, a shorter support tower 14 can be employed. Also, since the feed wires themselves serve as a feed line support catenary, the overall load which the catenary 18 has to support is reduced, thereby enabling the construction of a main support catenary with considerably less curvature or sag, which in turn enables the use of a shorter tower.

The The catenary 18 is constructed so that it, together with the support provided by the feedline 55, is capable of carrying the entire antenna load. In the particular embodiment shown in FIG. 2 in which all the elements are perpendicular to the ground surface, the catenary 18 is positioned above ground to insure that at each point at which a top end of a dipole element is to be coupled thereto there exists a free space distance from the ground which is at least equal to the dipole 's physical length.

As seen in FIGS. 2 and 3, the catenary 18 is above ground so that the longest element 69 is suspended in the vertical plane with its end 6% directly coupled to the catenary l8 and its lower end 690 at or near ground 12. As previously indicated, the other elements are directly coupled to the catenary 18 at their top ends. The bottom ends of most of the long elements are close to ground 12 so that very short individual wires can be used to secure the bottom ends of the elements to ground. These wires are generally designated by numeral 71.

Due to the curved design of the feedline 55, the apex 60 is above ground, unlike the apex in the prior art VPLPA, such as the one shown in FIG. 1, in which the apex 60 is at ground level. Consequently, the bottom ends of a significant number of the shorter dipole elements, near the array front end, are above ground. The bottom ends of these elements may be secured to ground by means of a ground support catenary 75, together with short drop rods 76 if necessary. It should be pointed out that having the apex 60 above ground is not a disadvantage. Rather, such an arrangement affords significant electrical advantages which may be summarized as follows. The elevation of the apex raises the phase center of the active elements at high frequencies, thereby narrowing the radiation pattern in the elevation plane, raising the antenna gain at those frequencies and directing the radiated energy toward those angles most useful in long distance communication at the higher frequencies.

101003 Mon wherein n+1 and n represent two adjacent elements, n+1 being closer to the array back end. L and X represent element physical length and distance from the apex, respectively.

Since in prior art, the feed wires are disposed-in a straight line, the distance X and X represent distances measured along a straight line from the apex.

In the present invention the distances X and X may be measured either along the curved feed line or along a straight horizontal line from the apex 60. Such a line represents an X axis. The relative lengths of the elements of the array of the present invention are generally controlled by a single value of 0', as is the case in the prior art. However, minor deviations from a can be tolerated without affecting the arrays electrical performance.

It should be pointed out that since the feed wires 55 are connected at the centers of the various dipole elements, these wires extend substantially across the center of the total antenna curtain, which for definition is assumed to include the array of the elements, the short connecting wires 71 and catenary 75. This is particularly true toward the back end of the array whereat the longer elements are located. Thus, each of the longer elements together with the wire 71 which connects its bottom end to ground is supported at or very near its center or midpoint. As is appreciated by those familiar with the art, by supporting an element at its center, the element structural load which has to be supported by the main support catenary is reduced by a factor of four for the most critical loading condition, which occurs under the action of strong winds. Thus, it should be apparent that the load support function of the feed wires is most significant, since it reduces significantly, the load to be carried by catenary 118.

Reference is now briefly made to FIG. 4 which is an isomet ric view ofa portion of the back end of the antenna. Therein the feed wires 55 are represented as transposed feed wires 55a and 55b. Each element, such as 61, is shown as a dipole comprising poles 61' and 611", connected to lines 55a and 551;, respectively. The transposition is accomplished by connecting alternate poles on each side of the feed wires to the same wire. Thus, pole 61, 62 and 63", etc., are connected to wire 55a and poles 61', 62" and 63', etc., are connected to wire 55b. As shown, the feed wires are assumed to be in a horizontal plane. However, it should be apparent that any other orientation of these wires may be assumed to facilitate their connections with the various radiating poles.

The foregoing described novel VPLPA, constructed in accordance with the teachings of the present invention may be summarized as comprising a plurality of dipole elements arranged to form a vertically polarized log-periodic array. The array is supportable by a support structure of minimum height and size, due to the use made of the feed wires to serve as a feed line-support catenary. This catenary carries part of the antennas structural load, thereby reducing the load support requirements of the antennas main support catenary. The latter is supported at a height above ground so that each of the dipole elements is suspendable above ground with the elements top end being in direct mechanical connection with the main catenary, rather than by means of drop rod. Assuming that the catenary 18 is constructed of an electrically conductive cable, each dipole is connected to the catenary in electrical insulation therefrom. Likewise, each element is secured to ground in electrical insulation therefrom.

The elimination of the drop rods greatly reduces the overall height of the antenna as well as the total antenna structural load, while the use of feed wires to act as a feed line catenary, which mechanically or structurally coacts with the main catenary in supporting the antenna, greatly reduces the main catenarys load support requirements. Consequently, a support catenary with reduced sag may be employed so that a shorter and smaller support structure is needed to support the antenna of the present invention.

From the foregoing it should be apparent that in prior art antennas the tower height is in the range of 1.34 of A2 of the lowest frequency of the design band. For example,

On the other hand in novel antennas of the present invention the tower height is considerably less. For example for a lowest frequency of 3 mc., the tower height'of feet is 1.1 times the )\/2 of the lowest frequency, since For an antenna with a lowest frequency of 2.5 mc., the tower height is 205 feet, which is 1.04 times one-half wavelength of 2.5 mc., since Thus, the novel antenna of the present invention may be defined as one with a tower height in the range of 1.1 of one half wavelength of the design frequency of the longest element in the array. For the scope of the invention, the novel antenna may also be defined as one in which the highest point of the antenna does not exceed a height H, where H is 1.2 times M2 of the design frequency of the longest element in the array.

Although particular embodiments ofthe invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. in a vertically polarized log-periodic antenna of the type designed for operation over a frequency band substantially varying from a first low frequency to a second high frequency, the antenna including feed means electrically coupled to a plurality of radiating means whose electrical lengths are selected as a function of the frequencies of signals in said frequency band at which the radiating means are to resonate, said radiating means forming an antenna array including a first radiating member of a length corresponding to a selected fraction of the wavelength of signals at said first lowest frequency and a second radiating member of a length corresponding to a selected fraction of the wavelength of a signal at said second highest frequency, the arrangement comprising:

antenna support means for supporting said antenna in a vertical plane by supporting said plurality of radiating members to extend from an array front end to an array back end, with said first radiating member positioned toward the array back end and the second radiating member toward said array front end; and

mechanical coupling means for mechanically coupling said antenna support means to said feed means, said feed means comprising a two-wire feeder, and each radiating means comprises a dipole connected at its mid portionto said two-wire feeder with alternate dipoles connected to a different wire of said two-wire feeder, said two-wire feeder being connected to said antenna support means as a support catenary so as to support a portion of the structural load of said antenna in said vertical plane.

2. The arrangement as recited in claim 1 wherein said antenna support means include at least first support means for supporting the array back end and second support means for supporting said array front end and said two-wire feeder is structurally connected by said mechanical coupling means to said first and second support means to form said support catenary so that the distance along said feed means between a first point of contact of said feeder with said first support means and a second point of contact of said feeder with said second support means is greater than the distance along a straight line between said first and second points of contact.

3. The arrangement as recited in claim 2 wherein said first support means comprises a tower, extending substantially vertically from a reference surface, each dipole having a first end upwardly disposed in said vertical plane and a second opposite end downwardly disposed in said vertical plane and said antenna support means include a main support catenary extending from said tower to said second support means and connecting means for directly connecting each dipole at substantially its first end to said main support catenary in electrical insulation therefrom.

4. The arrangement as recited in claim 3 wherein each dipole has a top pole directly connected to said two-wire feeder and to said main support catenary, and a bottom pole having one end connected to said twowire feeder and an opposite end, and means for coupling opposite ends of said bottom poles to said reference surface.

5. The arrangement as recited in claim 2 wherein the height of said tower is in the range of 1.1 of the length of said first dipole in the vertical direction.

6. In a broadband vertically polarized log-periodic antenna of the type which includes a plurality of radiating dipoles of different lengths, arranged in a substantially log-period array, the array including at its back end a longest dipole whose length is a function of the wavelength of signals of the lowest frequency in the design band and a shortest dipole at the array front end, whose length is a function of the wavelength of signals of the highest frequency in the design band and a twowire feed line, a support arrangement comprising:

a support tower vertically positioned above a reference surface;

a front support pole vertically positioned above said reference surface;

a main support catenary extending between said tower and said from support pole; and

coupling means for coupling said feed line to said tower and to said pole and for coupling said dipoles to said main support catenary and to said feed line at the centers thereof with alternate dipoles coupled to a different wire of said two-wire feed line, with said feed line being coupled to said tower and to said pole to form a secondary support catenary so as to bear part of the antenna load in said vertical plane.

7. The arrangement as recited in claim 6 wherein said coupling means further include means for coupling substantially all dipoles directly to said main support catenary without drop rods therebetween.

8. A broadband vertically polarized log-periodic antenna comprising:

an array of dipoles each being substantially )t/in length where A is the wavelength of the signals of a frequency at which the element is to radiate most strongly;

a two-wire feed line electrically and mechanically coupled to the two poles of each dipole at the dipole center with corresponding poles of alternate dipoles connected to the same wire; and

an antenna support structure for supporting said dipoles in a substantially vertical plane to form a substantially vertically polarized log-periodic array, said support structure including a main support tower substantially vertically positioned above a reference surface, with ends of said feed line being mechanically connected to said antenna support structure so as to form a support catenary, whereby said feed line acts as a load-bearing member in said vertical plane. 9. The antenna as recited in claim 8 wherein said support structure includes a support pole with said feed line being connected to the support pole and to said tower to form said support catenary to support at least a portion of its own structural load.

10. The antenna as recited in claim 9 wherein the support structure includes a main support catenary and said dipoles are coupled to said feed line with one pole of each dipole extending above said feed line and defining a top pole and the other pole extending below the feed line and defining a bottom pole and means for coupling the top pole of substantially every dipole directly to said main support catenary.

11. The arrangement as recited in claim 10 wherein H defines the height of said tower, H being less that 1.3 times the length of the largest dipole in said array. 

1. In a vertically polarized log-periodic antenna of the type designed for operation over a frequency band substantially varying from a first low frequency to a second high frequency, the antenna including feed means electrically coupled to a plurality of radiating means whose electrical lengths are selected as a function of the frequencies of signals in said frequency band at which the radiating means are to resonate, said radiating means forming an antenna array including a first radiating member of a length corresponding to a selected fraction of the wavelength of signals at said first lowest frequency and a second radiating member of a length corresponding to a selected fraction of the wavelength of a signal at said second highest frequency, the arrangement comprising: antenna support means for supporting said antenna in a vertical plane by supporting said plurality of radiating members to extend from an array front end to an array back end, with said first radiating member positioned toward the array back end and the second radiating member toward said array front end; and mechanical coupling means for mechanically coupling said antenna support means to said feed means, said feed means comprising a two-wire feeder, and each radiating means comprises a dipole connected at its mid portion to said two-wire feeder with alternate dipoles connected to a different wire of said twowire feeder, said two-wire feeder being connected to said antenna support means as a support catenary so as to support a portion of the structural load of said antenna in said vertical plane.
 2. The arrangement as recited in claim 1 wherein said antenna support means include at least first support means for supporting the array back end and second support means for supporting said array front end and said two-wire feeder is structurally connected by said mechanical coupling means to said first and second support means to form said support catenary so that the distance along said feed means between a first point of contact of said feeder with said first support means and a second point of contact of said feeder with said second support means is greater than the distance along a straight line between said first and second points of contact.
 3. The arrangement as recited in claim 2 wherein said first support means comprises a tower, extending substantially vertically from a reference surface, each dipole having a first end upwardly disposed in said vertical plane and a second opposite end downwardly disposed in said vertical plane and said antenna support means include a main support catenary extending from said tower to said second support means and connecting means for directly connecting each dipole at substantially its first end to said main support catenary in electrical insulation therefrom.
 4. The arrangement as recited in claim 3 wherein each dipole has a top pole directly connected to said two-wire feeder and to said main support catenary, and a bottom pole having one end connected to said two-wire feeder and an opposite end, and means for coupling opposite ends of said bottom poles to said reference surface.
 5. The arrangement as recited in claim 2 wherein the height of said tower is in the range of 1.1 of the length of said first dipole in the vertical direction.
 6. In a broadband vertically polarized log-periodic antenna of the type which includes a plurality of radiating dipoles of different lengths, arranged in a substantially log-period array, the array including at its back end a longest dipole whose length is a function of the wavelength of signals of the lowest frequency in the design band and a shortest dipole at the array front end, whose length is a function of the wavelength of signals of the highest frequency in the design band and a two-wire feed line, a support arrangement comprising: a support tower vertically positioned above a reference surface; a front support pole vertically positioned above said reference surface; a main support catenary extending between said tower and said front support pole; and coupling means for coupling said feed line to said tower and to said pole and for coupling said dipoles to said main support catenary and to saiD feed line at the centers thereof with alternate dipoles coupled to a different wire of said two-wire feed line, with said feed line being coupled to said tower and to said pole to form a secondary support catenary so as to bear part of the antenna load in said vertical plane.
 7. The arrangement as recited in claim 6 wherein said coupling means further include means for coupling substantially all dipoles directly to said main support catenary without drop rods therebetween.
 8. A broadband vertically polarized log-periodic antenna comprising: an array of dipoles each being substantially lambda /in length where lambda is the wavelength of the signals of a frequency at which the element is to radiate most strongly; a two-wire feed line electrically and mechanically coupled to the two poles of each dipole at the dipole center with corresponding poles of alternate dipoles connected to the same wire; and an antenna support structure for supporting said dipoles in a substantially vertical plane to form a substantially vertically polarized log-periodic array, said support structure including a main support tower substantially vertically positioned above a reference surface, with ends of said feed line being mechanically connected to said antenna support structure so as to form a support catenary, whereby said feed line acts as a load-bearing member in said vertical plane.
 9. The antenna as recited in claim 8 wherein said support structure includes a support pole with said feed line being connected to the support pole and to said tower to form said support catenary to support at least a portion of its own structural load.
 10. The antenna as recited in claim 9 wherein the support structure includes a main support catenary and said dipoles are coupled to said feed line with one pole of each dipole extending above said feed line and defining a top pole and the other pole extending below the feed line and defining a bottom pole and means for coupling the top pole of substantially every dipole directly to said main support catenary.
 11. The arrangement as recited in claim 10 wherein H defines the height of said tower, H being less that 1.3 times the length of the largest dipole in said array. 